Production of chromium ammonium chloride complexes



Patented May 17, 1949 PRODUCTION OF .CHROMIUM AMLIONIUM CHLORIDE COMPLEXES Ljubomir W. Skala, Chicago, "111., assignor of sixty percent to M. M. Warner-and ten per cent'to Henry .Blech, Chicago, 111.

No Drawing. Application June'l, 1944, SeriaLNo. 539,182

6 Claims. .1

The invention relates to the electrodeposition of chromium and particularly to .a method for producinga complex chromium compound of the purpeo and luteo type suitable for electrodeposition of metallic chromium.

Although luteo .and purpeo chromium compounds are known, up to now there is no reference in the literature that metallic chromium was deposited from such compounds by electric current.

Toany one skilled in the art it is known that the chromium purpeo and luteo compounds are chemical combinations of tri-valent chromium with coordinated valencies as shown by Werners theory.

It *isalso known that the electrodeposition of metallic chromium in spite of all attempts was not a practical success up .to the present time. By using the complex chromium ammonium combinations and by observing certain rules indicated hereinafter in producing such complex chromium ammoniumcombinations the metallic .chromium of the tri-valent type may be easily extracted and depositedelectrochemically in the same way as .for instance silver is deposited from ,a complex sodium or potassium-silver-cyanide solution.

The difference between the electrodeposition of chromium metal from such-a complex chromium ammonium combination .and that from chromic trioxideis a basiccne.

In chromic acid which is formed when chromic trioxide is dissolved in water the chromium ion isin combination with a radical represented as an anion, the kation being the hydrogen ion.

It is, therefore, necessary'before isolating the metallic chromium from .the aforesaid solution to bring or to transform the chromium ion from the anion group into the kation group to make the deposition for the chromium on the cathode possible.

This can be accomplished by the addition of certain agents, such as sulphuric acid or hydrofluoric acid, or certain fluorides. The purpose of these agents and the mechanics of their action is at present not very well understood.

The chromium metal deposited from such a solution is of the hexa-valent type, the deposition of which requires a much greater electrical energy than would be necessary for detachment of a trivalent chromium ion.

It is, therefore, evident that if the chromium -ion would be originally in the kation group of a chromium chemical combination, such as is the case in the complex chromium ammonium combination, such a chromium ionwould behave entirelydifferently under electric currentthan that of the chromic acid solution.

In other .words such chromium ion would follow the electrochemical laws established for the more common metallic ions such as copper, nickel and others.

In practice this means .thatmetallic chromium may be deposited from such type solutions with less energy, with better throwing power, and less erratic behavior of the electrolytic bath.

The complex chromium ammonium combinationof the luteo and gpurpeo type were disclosed previously and are possible to be produced by widely difierent processes such .as direct combination of chromic chloride with liquid ammonia (as described by Schlesinger) or by oxidationof chromous chloride as described originally by Joergensen, Christensen, and subsequently by Mellor.

However, whatever method of production is used the fact has been established that no prior method .made possible the electrodeposition of metallic chromium from the aforementioned complex chromium combination.

The reason for this is, that a chromium ammonium complex combination of the purpeo or luteo type is produced from intermediate materialsuch as chromic or chromous chloride, sulphate, etc., by either direct combination with ammonia such as described by Schlesinger or from .chromic or chromous chloride, sulphate, etc,, produced by an intermediate compound such as described by Joergenson, Mellor and others.

It is well known that chromic or chromous chloride or sulphate are not simple type combinations but that they are in fact a mixture of the a, ,3 and 'y sub-types.

It is, therefore, evident that if e. g. a commercial chromic or chromous chloride is taken asa'base for production of a complex chromium ammonium combination, the resulting complex combination can never be of a uniform structure but will contain the characteristics of the intermediate combination.

Only "then if a complex chromium ammonium combination is produced from chromic or chromous derivatives of uniform structure can we expect-that such a complex chromium ammonium combination will be also uniform.

It is, therefore, imperative that a perfect control of production of the intermediate chromic or chromous chloride be exercised.

There are many factors entering in the production of such complex chromium ammonium combinations, such as temperature, time, im-

purities, and others which will be evident from the following description.

It is, therefore, the main object of my invention to provide a practical chemical combination and, consequently, a corresponding solution which will eliminate the disadvantages of the chromic trioxide solution and render electrodeposition of chromium more similar to metals such as copper, nickel, silver, etc. It is a further object of my invention to utilize for the el'ectrodeposition of chromium such chemical compositions or salts which, when dissolved in water, will disassociate electrolytically in such a Way that the chromium ion is in the kation group.

It is evident that such a chemical composition will represent a complex metallic compound, in this case chromium compound or salt.

Werners studies of such complex metallic ammonium compounds show the important fact that the electrolytic disassociation of Cr(NH3) 6014 may be represented by an equation and the electrolytic disassociation of Cr(NH3) 5013 is represented by the equation [Cr (NE) 5011 Cl2= It is evident from the above equations that in the above cases the positive chrome ion Cr+ is in the complex kation group and must therefore in the electrolysis of the solution travel and be neutralized on the cathode, whereas the negative chlorine ion Cl is neutralized at the anode.

Of course, this assumption is strictly of a theoretical nature, which requires certain coordination with other factors in practice.

The following is the specification of an improved chemical process by which it is possible to obtain continually and most economically the complex chromium-ammonium compounds.

It is well known to the students of this group of complex compounds that the original production of them, as described in literature, is not only of the laboratory experiment type but also of a very erratic and inconsistent nature with no predictable results in the majority of cases. As previously mentioned the erratic nature is a consequence of the complexity of the intermediate product taken by previous workers at the starting point.

The known theoretical principle for the production of the complex chromium-ammonium compounds is quite simple. An inexpensive chromium salt, such as K2C12O7 (potassium bichromate) is reduced by known means first to a chromic salt in solution such as CXCls. The chromic salt in turn is reduced to a chromous salt CIC12 in solution. This chromous solution is introduced into a mixture of ammonia (NI-I3) solution with an excess of solid ammonium chloride (NHiCl).

This ammonia and ammonium chloride mixture with the introduced chromous chloride solution is kept for a certain time and Without the access of air, in a closed container, where the oxidation of the bivalent chromium into a trivalent chromium takes place, by decomposing the water and acquiring the hydroxyl (OH) group, thus changing first into a basic complex chromium ammonium compound and, in turn, into a correspondin normal chromium ammonium compound, of the type Cr(NI-I3)5Cl3 which is of rose color and thus known as chromium purpeo salt.

Joergensen showed that if the above specified mixture is kept under a. lowered temperature, say from zero to 19, a different chemical compound is produced which deposits as yellow crystals and which can be represented by the formula so-called luteo chloride. He also showed that both of these complex compounds are soluble in water, but insoluble in alcohol, and therefore could be extracted, re-crystallized, and thus obtained in pure form from the ammonia-ammonium-chloride mixture.

The method of converting the basic material (in our case, potassium bichromate K2Cr2O'z) into the final complex chromium compound, including the necessary ammonium chloride (NI-I401) is as follows:

The integral part may be carried out by utilizing various well known reducing and oxidizing processes singly or in combination. For example, the first reduction of potassium bichromate (K2CI'2O7) to chromic chloride (CICls) in solution may be carried out according to the equation.

utilizing ethyl alcohol and hydrochloric acid.

The resulting chromic chloride produced by this method is of very complex type as Was proven by previous workers, and contain the sub-type groups of u chromic chloride, ,8 chromic chloride, and 'y chromic chloride, each of these sub-type chromic chlorides having different electro-chemical characteristics. If We convert chromic chlorides thus produced into chromous chloride utilizing for instance metallic zinc (Zn) as a reduction means according to the equation:

We will obtain a blue solution of chromous chloride (C1C12) which chromous chloride is of a complex type following the characteristics of the subtypes of the chromic chloride.

It was established that the zinc utilised in the reduction of potassium bichromate in the presence of hydrochloric acid and converting said bichromate into chromous chloride is an important factor in influencing and determining not only the intermediate chromous chloride product but also the final complex chromium ammonium product.

It was further established that it is imperative to use two forms of metallic zinc in the reaction.

These two forms of metallic zinc are the solid and the mossy or porous zinc. It also was established that the ratio of quantities of these two forms of zinc is determinative for the speed of the reaction, the temperature under which the reaction takes place, and the length of time durin which the reaction occurs. The speed and temperature of the reaction is determined by the mossy or porous form of the zinc, whereas the length or the duration of the reaction is determined by the solid zinc.

It is evident to one skilled in the art that the purity of both forms of zinc employed is also a determining factor in the production of the intermediate chromous chloride, and, therefore, it is necessary to use both forms of zinc free from impurities.

The producing of the intermediate chromous chloride is thus dependent upon the speed, the length of time of the reaction, and furthermore upon the temperature under which the reaction is carriedi' out, and which? factors: inltur'n. are; dc. pendent from the form andipurity ofthezinc.

Itis nowevident thatrif sucir chromous: chloride CIClz is transferred withouttacoessofi'air into a mixture of ammonia-ammonium chloride, where the oxidation of theibivalent chromium (Cr++) intoa trivalent. chromium" (C'r+++). takes place,

the: resulting chemical: combination. .will. not; be: a

uniform. complex. chromium-ammonium combination butLaimiXture of complex chemical combinations: following the characteristics of :the subtypes oft the starting. material; in ourcase the chromic chloride. CrClz.

It will be notedthat withrthe:chromous chloride. (GICIa) solution is also transferred the. zinc chloride- (ZnClz) which was producediduring reduction ofchromic chloride (CrClsl with zinc;

This zinc chloride is-very bothersome in the oxidation ofthec'hromous chloride (CrClz) and.

also inlthe correspondent process\ of procuring M thefinal complex chromium-ammonium.

It is truethatit can be separated from the final complex chromiumrammonium compound to obtain a. pure complexcompound, but for the purpose of using such. a complex chromium.- ammonium compound. in electrodeposition of chromium metal, I findiitlimperative to separate the. zinc chloride. (ZhClzlby aseparate chemical process interpolated-in my method I also find. it necessary immy methodof continuous production. of the complex chromiumammonium. compounds tocoordinate the variouschemical processesutilized in converting the raw material (potassium bichromate) into the final product as follows:

Finely, granulated potassium bichromate ('K2Cr2O'z) is placed into alarge: container with an excess of zinc (Zn), and diluted hydrochloricacid (HCl) is allowed to run into the mixture. In my experiments I found that the hydrochloric acid should' be diluted in the ratio of 2:3 and should be preheatedto an optimum temperature between 45 and 50C. A violentv reactiontaltes" place :in the firstffew minutes, whichreduces the potassium bichromate first intoadeep green solution of chromic chloride (CI'Cls). Then the re action'quiets down, and inten to fifteenminutes thereaction is finished: and the solution turnsi intoa clear blue color, namely that. of chromous chloride (CrCh); This solution, as previously mentioned, contains also the zinc chloride (ZnClz).

The excess of developed. hydrogen (H) during the. reaction is carried away through a water sealv to protect the chromous chloride (CJrClz) solution from oxidation by air;

It is imperative that this reaction is carried out without the least trace of atmospheric oxygen, therefore, it must-be carried out man inert atmosphere such as carbon dioxide (CO2), nitrogen (N), hydrogen (H) or any other inert gas, which inert gases must be of the highest purity produced by corresponding washing. Any impuritiesv in the atmosphere in which the aforesaid reactionis taking place will have anefiect upon the characteristic of the chromic or chromous chloride so produced. It is further important that the reaction temperature during? thereduction-iskept constant; It is further im portantthat all the impurities fromthe reaction. entering factors are eliminated especially the impurities inthe metallic zinc.

In the course of. my-experiments- I also foundout that two types'of metallic. zinc should be.-

used: The mossy type andthe solid type. The

reason forthissispthat: if only one typ'e of zinc= is used. the reaction will be either" too; fastor too1 Cslow, thus affecting.thecharact'eristic of the: yre

Itis evident that after theraforementioned re:- duction there isa mixture of: chromous: and zinc chloridesin the: reaction; chamber;

The: next step. in the processing; of: the. blues chromous chloride (GrClrl containing the' zinc:

chloride (Z'nClz) consists. of! bringingv the blue:

solution to" contact? with-a saturated solution: ofr sodium acetate (NaCI-ISOQBHzO) This operation is also carried out in: an:atmos-- phere of: carbon dioxide orother inert gas. A red precipitate of chromousacetate,

Cr2(C 2'H302) 6.21120" is. the result, the zinc chloride remaining inthe' solution.

After the precipitate settles down the supernatant liquid containing the zinc chloride. and: other soluble impurities is decanted-and the pre cipitate is washed under agitation with water saturated. with carbon dioxide (CO2) and water acidifiedwithacetic acid. (CH3.C0OH) The red. chromous acetate, Cr2(C2I-IsO29 c.2I-I2n is'practically insoluble in such washing water and,- therefore, it may beientirely. separatedlfrom. all impurities, particularly zincjust-by. repeated? washing with acidifiedand. carbondioxide. (CO2) saturated. water.

After the finalwashing theflprecipitate is. ale lowed to settle, the washing, water decanted, and? the container filled with carbon dioxide (CO2) or other inert gas. Inthis inert atmosphere concentrated hydrochloric acid (HCl) is allowed into the container, which acid dissolves the precipitate, forming a blue solution of chromous chloride (CrClzl without any zinc on metallic impurities. The zinc may be recovered from the supernatant liquid and from the wash-water by precipitation with alkali carbonates as a byproduct.

It is important that the' aforementioned washing of the chromous acetate and the consequent dissolving thereof in hydrochloric: acid' is shielded from any traces: of oxygen, forit iswell known; that chromous chloride is extremely sensitive to oxygen;

The pure solution of chromous chloride (CrCl2) may. be again stored. inquantities in an atmosphere ofcarbon dioxide (CO2) or other inert gast. or it may be processed -further without delay.

A. portion of the pure chromous chloride: (CrClzl solution is placed in a: container, the temperatureof whichis brought'up to 68- C. Dur ing the application of heat; tothecontainer, the: same: is evacuated and the concentration ofthe chromous chloride (CrClzl solution takesplacea and is carriedtothe*poihtwhen the crystallizaw tion starts to take place.

In my experiments I foundout that a mucl'i i better method thanzthe use of vacuumis to connect the vessel containing the chromous chloride? and to which the heatis appl-ied' with a source of pure nitrogen gas. andto-provide the outlet of the vessel with a-:water seal-thuscarrying out theconcentration of the=so1ution in an inert at'-- mosphere.

Whenthe proper construction of the chromous chloride (CIC12) solution= is reached the same is transferred. in an atmosphere of nitro-'- gen (N) or hydrogeniI-D but notofcarbon dim oxide (CO2), into a vessel containing a mixture of solid ammonium chloride (NHCD and concentrated ammonia water. I

The vessel is sealed with a water seal and placed in a constant temperature water bath. The liquid in the vessel, which has a blue color after the transfer, turns gradually depending upon the temperature into a deep red color and hydrogen is developed, escaping through the water seal, which seal also prevents the oxygen of the air from coming in contact with the mixture. When the development of hydrogen (H) ceases, the process is ended and the liquid filtered into a storage tank or directly into the crystallization pans.

The ammonia chloride crystals remaining in the vessel are washed once or twice with cold water and the resulting reddish liquid stored in a separate tank. This liquid contains mostly the complex chromium ammonium salts of the luteo and roseo type, depending, as previously said, on the temperature maintained during the oxidation process in the water bath. It may be added to the mother liquid or it may be crystallized separately.

The crystallization pans are placed in a dust free room and in a current of dry pre-heated air. The crystallization begins very shortly and is carried up to the point when all the liquid is evaporated and dry flakes of violet color are left in the crystallization pans.

These crystalline flakes dissolve easily in cold water and re-crystallization process may be employed. The composition of these crystals may be formulated as follows:

Chromium pentamino trichloride (purpeo) (Cr(NHa) sCls) Chromium hexamino trichloride (luteo) (Cr (NHa) eCls) Ammonium chloride (NHiCl) In carrying out the process reference has been made to complex chromium compounds of the purpeo and luteo type which theoretically as most suitable material for the electrodeposition of chromium.

During the experiments I found out that only the purpeo type is suitable for electrodeposition and consequently that it is necessary to promote the formation of the purpeo type and prevent the formation of the luteo type during the reaction of chromous chloride with ammonia in the presence of ammonium chloride.

This can be very easily achieved by close control of the temperature of the reacting solutions. It is well known that if the temperature is allowed to drop under 18 C. the formation of the luteo predominates. If, however, the reacting solution is kept above 18 C. the formation of the purpeo type predominates.

I further found out that the optimum temperature is between the limits of C. to C.

It is furthermore important that this temperature be kept constant during the entire reaction time.

While the specification describes a compound suitable for electrodeposition of chromium and the method of producin such compound, numerous changes in replacing the anion group by a different radical may be made without departing from the invention.

I, therefore, claim my invention as broadly as the state of the art permits.

I claim:

1. The method of producing a complex chromium ammonium chloride combination suitable for electrolytic deposition of chromium metal, including the steps of converting potassium bichromate in the presence of hydrochloric acid by specific reduction agents comprising predetermined quantities of zincs of the solid and mossy or porous type to a bivalent chromium chloride compound, converting further said bivalent chr0- mium chloride compound into a bivalent chromium acetate compound, separating said acetate compound by washing and filtration from the solution and oxidising said bivalent compound to a trivalent complex chromium in reaction with ammonia, ammonium chloride and water and separating the ammonium chloride crystals from the resulting product by repeated washings.

2. The method of producing a complex chromium ammonium chloride combination suitable for electrolytic deposition of chromium metal, including the steps of converting potassium bichromate by bringing said bichromate in chemical reaction with hydrochloric acid and a mixture of chemically pure solid and porous zinc particles to a bivalent chromium chloride compound, converting further said bivalent chromium chloride compound into a bivalent chromium acetate compound, separating said acetate compound by Washing and filtration from the solution and oxidising said bivalent compound to a trivalent complex chromium in reaction with ammonia, water, and ammonium chloride, said steps being carried out in accordance with predetermined temperature, time and speed of reactions and separating the ammonium chloride crystals from the resulting product by repeated washings,

3. The method of producing complex chromium ammonium chloride combinations suitable for electrolytic deposition of metallic chromium, including the steps of placing potassium bi-chromate into a mixture of hydrochloric acid and a mixture of solid and porous metallic zinc, bringing the resulting chromous chloride and the zinc chloride in reaction with a saturated solution of sodium acetate thus removing from the precipitate all residual zinc compounds, and separating the precipitate of chromous acetate from the solution by filtration, adding hydrochloric acid to convert the formed chromous acetate into pure chromous chloride, heating the chromous chloride to concentrate it, mixing it with a mixture of solid ammonium chloride and concentrated ammonia water, and crystallizing the liquid after the oxidation free from access of air of the mixture is completed and separating the ammonium chloride crystals from the resulting product by repeated washings.

4. The method of producing complex chromium ammonium chloride combinations suitable for electrolytic deposition of chromium metal, including the steps of placing finely granulated potassium bichromate into a mixture of hydrochloric acid and a mixture of solid and porous metallic zinc acting as a reducing agent bringing the re-- sulting chromous chloride and zinc chloride in reaction with a saturated solution of sodium acetate thus removing from the precipitate all soluble zinc compounds, and separating the precipitate of chromous acetate from the solution by filtration, adding hydrochloric acid to obtain pure chromous chloride, heating the chromous chloride to concentrate it, mixing it with a mixture of solid ammonium chloride and concentrated ammonia water, and crystallizing the liquid after the oxidation free from access of air of the mixture is completed and separating the ammonium chloride crystals from the resulting product by repeated washings.

5. The method of producing complex chromium ammonium chloride combinations suitable for electrolytic deposition of chromium metal, including the steps of placing potassium bi-chromate into a mixture of hydrochloric acid and a mixture of solid and porous metallic zinc acting as a reducing agent, bringing the resultingchromous chloride and the zinc chloride in reaction with a saturated solution of sodium acetate in an atmosphere of inert gas thus removing from the precipitate all soluble zinc compounds, and separating the precipitate of chromous acetate from the solution by filtration, adding hydrochloric acid to obtain pure chromous chloride, heating the chromous chloride to concentrate it, mixing it with a mixture of solid ammonium chloride and concentrated ammonia water, and crystallizing the liquid after the oxidation free from access of air of the mixture is completed and separating the ammonium chloride crystals from the resulting product by repeated washings.

6. The method of producing chromium ammonium chloride combinations suitable for electrolytic deposition of chromium metal, including the 10 steps of converting intermediately an alkaline bichromate in the presence of hydrochloric acid and a mixture of constant ratio oi solid and porous metallic zinc to a trivalent chromic chloride and subsequently into a bivalent chromous chloride, converting said chromous chloride into a water insoluble chromous acetate, eliminating impurities by repeated washing and separating the precipitate of chromous acetate from the solution by filtration, reconverting said chromous acetate to chromous chloride, introducing the pure chroous chloride into a mixture of solid ammonium chloride and ammonia water, subjecting said mixture to a constant temperature, and after the reaction is completed subjecting said mixture to crystallization and separating the ammonium chloride crystals from the resulting product by repeated washings.

LJUBOMIR W. SKALA.

REFERENCES CITED The following references are of record in the file'of this patent:

UNITED STATES PATENTS Name Date Hurd Feb, 18, 1947 OTHER REFERENCES Number 

